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Newt

From Wikipedia, the free encyclopedia
This article is about the animal. For other uses, seeNewt (disambiguation).
"Eft" redirects here. For other uses, seeEFT.

Newt
Temporal range:Late Cretaceous–Recent[1]
Alpine newt
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Urodela
Family: Salamandridae
Subfamily: Pleurodelinae
Genera

14–17extantand sixfossilgenera, see text

Anewtis asalamanderin thesubfamilyPleurodelinae.The terrestrial juvenile phase is called aneft.Unlike other members of the familySalamandridae,newts aresemiaquatic,alternating between aquatic and terrestrial habitats. Not all aquatic salamanders are considered newts, however. More than 100 known species of newts are found in North America, Europe, North Africa and Asia. Newtsmetamorphosethrough three distinct developmental life stages: aquaticlarva,terrestrial juvenile (eft), and adult. Adult newts havelizard-like bodies and return to the water every year to breed, otherwise living in humid, cover-rich land habitats.

Newts are threatened byhabitat loss,fragmentationandpollution.Several species are endangered, and at least one species, theYunnan lake newt,has becomeextinctrecently.

Etymology[edit]

Two grey newts, taken from the front, under water, presumably in an aquarium
Pleurodeles,including theIberian ribbed newt,is the type genus of subfamily Pleurodelinae.

TheOld Englishname of the animal wasefte,efeta(of unknown origin), resulting inMiddle Englisheft; this word was transformed irregularly intoeuft,evete,orewt(e).The initial "n" was added from the indefinite article "an" byprovection (juncture loss)( "an eft" → "a n'eft" →...) by the early 15th century.[2]The form "newt" appears to have arisen as a dialectal variant ofeftinStaffordshire,but entered Standard English by the Early Modern period (used by Shakespeare inMacbethiv.1).[3]The regular formeft,now only used for newly metamorphosed specimens, survived alongsidenewt,especially in composition, the larva being called "water-eft" and the mature form "land-eft" well into the 18th century, but the simplex "eft" as equivalent to "water-eft" has been in use since at least the 17th century.[4]

Dialectal English and Scots also has the wordask(alsoawsk,eskin Scots[5]) used for both newts andwall lizards,from Old Englishāþexe,fromProto-Germanic*agiþahsijǭ,literally "lizard-badger" or "distaff-like lizard" (compare GermanEidechseandEchse,both "lizard;"*agi-is ultimately cognate with Greekὄφις"snake," fromProto-Indo-European*h₁ogʷʰis[6]). Latin had the namestelliofor a type of spotted newt, now used for species of the genusStellagama.Ancient Greek had the nameκορδύλος,presumably for the water newt (immature newt, eft).[7]German hasMolch,fromMiddle High Germanmol,wikt:olm,like the English term of unknown etymology.

Newts are also known asTritones(viz., named for the mythologicalTriton) in historical literature, and "triton" remains in use as common name in some Romance languages, such as Spanish and Romanian, but as well as in Greek, Russian, and Bulgarian. The systematic nameTritoneswas introduced alongside Pleurodelinae byTschudiin 1838, based on the type genus namedTritonbyLaurentiin 1768. Laurenti'sTritonwas renamed toTriturus( "Triton-tail" ) byRafinesquein 1815.[8]Tschudi's Pleurodelinae is based on the type genusPleurodeles(ribbed newt) named byMichahellesin 1830 (the name meaning "having prominent ribs," formed fromπλευρά"ribs" andδῆλος"conspicuous" ). Collective nouns for newts are flotilla and armada.

Distribution and habitats[edit]

A brown newt under water, on gravel
ThePyrenean brook newtlives in small streams in thePyreneesmountains.

Newts are found in North America, Europe, North Africa and Asia. ThePacific newts(Taricha) and theEastern newts(Notophthalmus) with together seven species are the only representatives in North America, while most diversity is found in the Old World: In Europe and the Middle East, the group's likely origin, eight genera with roughly 30 species are found, with theribbed newts(Pleurodeles) extending to northernmost Africa. Eastern Asia, from Eastern India over Indochina to Japan, is home to five genera with more than 40 species.[citation needed]

Newts aresemiaquatic,spending part of the year in the water for reproduction and the rest of the year on land. While most species prefer stagnant water bodies such as ponds, ditches, or flooded meadows for reproduction, some species such as theDanube crested newtcan also occur in slow-flowing rivers. TheEuropean brook newts(Calotriton) andEuropean mountain newts(Euproctus) have even adapted to life in cold, oxygen-rich mountain streams. During their terrestrial phase, newts live in humid habitats with abundant cover such as logs, rocks, or earth holes.[citation needed]

Strikingly red eft on a rocky underground
Green newt with red spots under water
Theeastern newtas terrestrialeft(left) and as an adult during aquatic breeding season (right)

Characteristics[edit]

Newts share many of the characteristics of their salamander kin,Caudata,including semipermeable glandular skin, four equal-sized limbs, and a distinct tail. The newt's skin, however, is not as smooth as that of other salamanders.[9]Thecellsat the site of an injury have the ability to undifferentiate,reproduce rapidly, and differentiate again to create a new limb or organ. One hypothesis is that the undifferentiated cells are related totumorcells, since chemicals that produce tumors in other animals will produce additional limbs in newts.[10]

Development[edit]

The main breeding season for newts (in the Northern Hemisphere) is in June and July. A single newt female can produce hundreds of eggs. For instance, the warty newt can produce 200–300 eggs (Bradford 2017). After courtship rituals of varying complexity, which take place in ponds or slow-moving streams, the male newt transfers aspermatophore,which is taken up by the female. Fertilized eggs are laid singly and are usually attached to aquatic plants.[citation needed]This distinguishes them from the free-floating eggs offrogsortoads,which are laid in clumps or in strings. Plant leaves are usually folded over and attached to the eggs to protect them. Thelarvae,which resemble fishfrybut are distinguished by their feathery external gills, hatch out in about three weeks. After hatching, they eat algae, small invertebrates, or other amphibian larvae.[citation needed]

During the subsequent few months, the larvae undergometamorphosis,during which they develop legs, and the gills are absorbed and replaced by air-breathing lungs.[11]Some species, such as the North American newts, also become more brightly colored during this phase. Once fully metamorphosed, they leave the water and live a terrestrial life, when they are known as "efts."[12][13]Only when the eft reaches adulthood will the North American species return to live in water, rarely venturing back onto the land. Conversely, most European species live their adult lives on land and only visit water to breed.[14]

Development in thenorthern crested newt(Triturus cristatus)
A transparent egg with a white embryo on the leaf of an aquatic plant
Embryo in jelly capsule
A newt larva with gills and forelimbs, but no hindlimbs developed
Young larva
A dark-coloured larva with all limbs developed but gills still apparent
Larva shortly before metamorphosis
A small, black newt without gills or crest on moss
Terrestrial juvenile
Newts lay their eggs on structures such as plants or stones under water. The larvae first develop fore- and later hindlimbs, and are strictly carnivorous. After metamorphosis, juveniles known aseftsemerge from the water and live a terrestrial lifestyle.

Toxicity[edit]

ThePacific newts(Taricha), including theCalifornia newt,are known for their toxicity.

Many newts producetoxinsin their skin secretions as a defence mechanism against predators.Tarichanewts of western North America are particularly toxic. Therough-skinned newtTaricha granulosaof thePacific Northwestproduces more than enoughtetrodotoxinto kill an adult human, and someNative Americansof the Pacific Northwest used the toxin to poison their enemies.[15]However, the toxins are only dangerous if ingested or otherwise enter the body; for example, through a wound. Newts can safely live in the same ponds or streams as frogs and other amphibians or be kept as pets. The only predators ofTarichanewts aregarter snakes,some having developed a resistance to the toxin. Most newts can be safely handled, provided the toxins they produce are not ingested or allowed to come in contact withmucous membranesor breaks in the skin.[15]

Systematics[edit]

Newts form one of threesubfamiliesin the familySalamandridae,asideSalamandrinaeandSalamandrininae.[16]They comprise mostextantspecies in the family, roughly 100, which are classified in sixteen genera:[17]

HypselotritonandLiangshantritonare regarded as separate genera by some authors, but this is not unanimous.[17]

The term "newt" has traditionally been seen as an exclusively functional term for salamanders living in water, and not aclade.Phylogeneticanalyses have however shown that species in the Salamandridae traditionally called newts do form amonophyletic group.[1][16][17]Other, more distantly related salamander families also contain fully or in part aquatic species, such as themole salamanders,theProteidae,or theSirenidae.

Classification of all genera of the Pleurodelinae subfamily after Pyron and Weins,[16]revised by Mikko Haaramo.

Phylogenetics[edit]

Phylogenetic analyses estimated the origin of the newt subfamily in theLate CretaceoustoEocene.[1]Severalfossil salamandershave also been referred to the Pleurodelinae, including:[18]

Anatomy and physiology[edit]

Circulation[edit]

The heart of newts, like that of most amphibians, consists of two atria and one ventricle.[19]Blood flows from the anterior and posterior caval veins into the right atrium; blood that entered the heart from the left atrium is then expelled out of the ventricle. Newts do not have acoronary arteryon the ventricle, due to circulation that is found in theconus arteriosus.Newts contain a special circulatory adaptation that allows them to surviveventricular penetration:when a newt's ventricle is punctured, the heart will divert the blood directly into an ascending aorta via a duct located between the ventricle and the conus arteriosus. Newts begin to regenerate the ventricle by a thickening of theepicardiallayer that protrudes to allow the new vessels to form, and conclude with a regeneration of the entiremyocardial wall.[19]

In early stages of development in amphibians, ventilator gas transport and hemoglobin gas transport are independent mechanisms and not yet coupled as they are in adulthood.[20]In juvenile amphibians, there is no cardiovascular response in conditions of hypoxia.[20]When newts are induced into anemia, they are able to respire without the need of blood cells.[21]InT. carnifex,around two weeks after anemia is induced, the newts produced a mass of cells that helps to revitalize the already circulating red blood cell mass.[21]

Respiration[edit]

Adult crested newts (Triturus cristus) were found to breathe mainly via the skin but also through the lungs and thebuccal cavity.Lung breathing is mainly used when there is a lack of oxygen in the water, or at high activity such as during courtship, breeding, or feeding.[22]

A form ofcompensatory respirationis the ability to release storederythrocyteswhen needed, for example underhypoxia.[23][24]Spleen size can increase as the temperature declines for adults – in larvae, there is no dramatic change in spleen size.[25]During hibernation, an increase in liver pigment cells allows for storage of oxygen, as well as other important ions and free radicals.[26]

Osmoregulation[edit]

In experiments, dehydratedeastern newtswere prone to a loss of motor control: After only 22% water weight loss, newts in the aquatic phase lost their ability to remain upright and mobile. However, after adaptation to a terrestrial phase, they could lose 30% before a loss of motor control was recorded. Newts in the terrestrial phase were found to dehydrate much quicker than newts in the aquatic phase, but conversely, during rehydration, dehydrated terrestrial animals will go through water gain 5x faster than dehydrated newts that are in the aquatic phase.[27]

In the Italian crested newt, it was shown that during winter months,prolactinis released into the circulatory system, which drives the newts into the aquatic environment and reduces the active transport of sodium ions.[28]In contrast to prolactin, which decreases osmotic permeability,vasotocinincreases the permeability and is secreted during the summer months.[29]Arginine vasotocin not only increases cutaneous water permeability, but promotes increased cutaneous blood flow.[30]

Thermoregulation[edit]

Thermoregulation, in combination with seasonalacclimation,describes the major mechanisms of how newts, asectothermscope with the changing temperatures existing in their environments. This regulation is most often achieved through behavioral thermoregulation.[31]They arethermoconformers,which means they will acclimate to their surrounding environmental temperatures.[31]When there is a large range of environmental temperatures, newts are insensitive to athermal gradient profile.[32]

To escape predators, newt larvae have been found to shift theirmicrohabitatto a temperature range that exists outside the predator's preferred temperature range.[33]Larvae that are in the metamorphosizing stage tend to prefer warmer temperatures than those in the stage following metamorphosis.[33]Therefore, the larvae in this stage will undergo a much more precise thermoregulation process than those in the intermediate stage.[33]

Reproductive females of the Italian crested newt were shown to regulate their body temperature more precisely and prefer higher temperatures than non-reproductive females and males.[34]

Spermatogenesis[edit]

The newt is regarded as an idealvertebratemodel for investigating the mechanism(s) controlling the transition frommitosistomeiosisduringspermatogenesis.[35]In the male newtCynopa pyrrhogaster,this transition was shown to involve expression ofPCNA,aDNA polymerase deltaauxiliary protein involved inDNA replicationandDNA repair,as well asDMC1protein, a marker forgenetic recombinationactivity.[35]

Susceptibility to pollution[edit]

Larvae, with their great number of lamellae in their gills,[36]are more susceptible to pollutants than adults.Cadmium,a heavy metal released into the environment from industrial and consumer waste, has been shown to be detrimental to theItalian crested newteven at a concentrations below Italian and European thresholds, by disrupting the activity of theadrenal gland.[37]In experiments allowing Italian crested newts to be exposed tononylphenol,anendocrine disruptorcommon in leakage from sewers, there was a decrease incorticosteroneandaldosterone,hormones produced by theadrenal glandand important for stress response.[38]

Conservation status[edit]

Panel of drawings of a red-black newt
TheYunnan lake newtis considered extinct.

Although some species, such as therough-skinned newt(Taricha granulosa) andEastern newt(Notophthalmus viridescens)in North America or thesmooth newt(Lissotriton vulgaris) in Europe, are still relatively common, populations of newts throughout their distribution range suffer fromhabitat loss,fragmentation,andpollution.This affects especially the aquatic breeding sites they depend on, but also their land habitats.[citation needed]Several species, such as theEdough ribbed newt(Pleurodeles poireti),Kaiser's spotted newt(Neurergus kaiseri), or theMontseny brook newt(Calotriton arnoldi) are considered threatened by theIUCN,and theYunnan lake newtis an example of a newt species that has gone extinct recently.[39]

Some newt populations in Europe have decreased because of pollution or destruction of their breeding sites and terrestrial habitats, and countries such as the UK have taken steps to halt their declines.[40][41]In the UK, they are protected under theWildlife and Countryside Act 1981and the Habitat Regulations Act 1994. It is illegal to catch, possess, or handlegreat crested newtswithout a licence, or to cause them harm or death, or to disturb their habitat in any way. TheIUCN Red Listcategorises the species as ‘lower risk’[14][42] Although the other UK species, thesmooth newtandpalmate newtare not listed, the sale of either species is prohibited under the Wildlife and Countryside Act, 1981.[43]

In Europe, nine newts are listed as "strictly protected fauna species" under appendix II of theConvention on the Conservation of European Wildlife and Natural Habitats:[44]

The remaining European species are listed as "protected fauna species" under appendix III.[45]

As bioindicators[edit]

Newts, as with salamanders in general and other amphibians, serve asbioindicatorsbecause of their thin, sensitive skin and evidence of their presence (or absence) can serve as an indicator of the health of the environment. Most species are highly sensitive to subtle changes in thepHlevel of the streams and lakes where they live. Because their skin is permeable to water, they absorb oxygen and other substances they need through their skin. Scientists study the stability of the amphibian population when studying the water quality of a particular body of water.[citation needed]

As pets[edit]

Chinese warty newts,Chinese fire belly newts,eastern newts,paddletail newts,Japanese fire belly newts,Chuxiong fire-bellied newts,Triturusspecies,emperor newts,Spanish ribbed newts(leucisticgenes exist), andred-tailed knobby newtsare some commonly seen newts in the pet trade. Some newts rarely seen in the pet trade arerough-skinned newts,Kaiser's spotted newts,banded newtsandyellow-spotted newts.[original research?]

References[edit]

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  45. ^"Annexe III: Protected fauna species".Retrieved2013-06-06.

External links[edit]

Look upnewtin Wiktionary, the free dictionary.
Look upnewtoreftin Wiktionary, the free dictionary.
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